Characterizing Soil Dissolved Organic Matter in Typical Soils from China Using Fluorescence EEM-PARAFAC and UV-Visible Absorption

Dissolved organic matter (DOM) strongly participates in a variety of critical environmental and ecological processes and has a large impact on environmental quality. In this study, ultraviolet-visible absorbance spectroscopy and excitation-emission matrices of fluorescence spectroscopy in combination with parallel factor analysis (EEMs-PARAFAC) were applied to characterize a total of 92 DOM samples extracted from four typical soil types under three different land-use regimes across China. DOC concentrations ranged from 6.52 +/- 1.09 to 25.62 +/- 4.83 mg L-1 and were generally higher in red soil from Guangdong and Guangxi, especially in paddy soil. Three fluorescence components were identified in soil DOM by EEMs-PARAFAC, including high molecular weight UVA humic-like substances (C1), low molecular weight autochthonous humic-like substances (C2), and protein-like substances (C3). DOM from black soil in Heilongjiang, purple soil from Sichuan, and red soil from Zhejiang had more humic-like substances, whereas DOM from yellow soil in Guizhou and red soil from Guangdong and Guangxi had lower degree of aromaticity and higher proportion of microbial-derived protein-like components (C3). Moreover, DOM from paddy soil tended to be more of protein-like components (C3) than that from other land uses and DOM from dryland soil generally had more autochthonous humic-like substances (C2). Our results demonstrated that soil DOM characteristics both varied significantly by soil type and land use, and EEMs-PARAFAC could be a useful approach to characterize the components and sources of heterogeneous DOM in soils.